The present invention relates to a drive slip control system.
Many different types of drive slip control systems exist. In principle, in drive slip control systems, the slip of the driven wheel in question is determined based on the wheel speeds, particularly by comparing the wheel speed of the driven wheel in question with a reference value that is determined based on the wheel speed of at least one non-driven wheel. This is compared with a maximum permitted slip, slip-reducing intervention in the torque of the vehicle""s drive unit and/or the wheel brake of the driven wheel in question being performed if the slip value of the driven wheel in question exceeds the maximum permitted slip threshold. A filter time used to filter the start of a slip control procedure, calculation of the slip threshold and/or the desired values transferred in order to control the torque of the drive unit and/or the amount of braking force applied to the spinning driven wheel by the control system are predefined or defined as a function of operating variables. A drive slip control system is described in, for example, German Patent Application 195 48 564 A1 (U.S. Pat. No. 5,884,719). German Patent Application 43 33 822 A1 (U.S. Pat. No. 5,562,569) describes a method of detecting a gearshift based on the engine speed and the wheel speed.
In certain applications, drive slip control systems may behave unsatisfactorily during a gearshift. This is because when the frictional connection between the engine and the drive train is reestablished following a gearshift, in particular an upshift, the driven wheels undergo a phase of high slip. This may cause the drive slip control system to be activated, which is disruptive, because it is associated with a short-term deterioration in traction. This effect may even be observed in cases where the coefficient of friction between the road and the tires is relatively high and in a normal situation the engine torque is not high enough to cause excess slip. Under special operating conditions during a gearshift, the excess slip is the result of additional power resulting from excessive engine speed, which must be reduced. Excessive slip occurs in particular when the engine speed is too high compared to the speed of the driven wheels. This arises in particular when the gearshift is performed too quickly and this is accompanied by an excessively slow drop in the engine speed or if the driver revs the engine before frictional connection is reestablished. The closure limitation functions of an engine control system also contribute to this, as they tend to cause the engine speed to drop slowly.
An object of the present invention is to provide a drive slip control system that displays improved characteristics during a gearshift.
The above and other beneficial objects of the present invention are achieved by providing a drive slip control system that displays considerably improved characteristics during a gearshift. Through measures that can be taken either independently or in combination with one another, under this special operating state the drive slip control system is rendered less sensitive than when under normal operating conditions, so that short-term drops in traction can be eliminated or at least diminished. As a result, traction is improved significantly during a gearshift.
Advantageously, driving stability, which is also assisted by a drive slip control system, is still maintained in critical driving situations, even during a gearshift. This is because the measures that render the drive slip control system less sensitive are only carried out if the vehicle is not in a stability-critical operating situation, such as, for example, during cornering. If the vehicle is in a stability-critical operating situation of this kind, the at least one measure that renders the control system less sensitive is wholly or partially cancelled.
It is particularly advantageous that the control system is rendered less sensitive continuously so that the transition is smooth and not noticeable to the driver.
It is particularly advantageous that the method described below can be used with automatic as well as manual transmissions.
Further advantages are set forth in the description below of the exemplary embodiments.